Alien reptiles on Mediterranean Islands: A model for invasion biogeography

First genetic insights of Gonatodescaudiscutatus (Reptilia, Gekkota) in the Galapagos Islands and mainland Ecuador

Studies on genetic variability amongst native and introduced species contribute to a better understanding of the genetic diversity of species along their autochthonous distribution and identify possible routes of introduction. Gonatodescaudiscutatus is a gecko native to western Ecuador and introduced to the Galapagos Islands. Despite being a successful species in human-modified habitats along its native and non-native ranges, neither the colonisation process nor the genetic diversity of this gecko is known. In this study, we analysed 55 individuals from 14 localities in western Ecuador and six localities in San Cristobal Island, Galapagos - the only island with a large, self-sustaining population. We amplified and analysed the genetic variability of two nuclear genes (Cmos and Rag2) and one mitochondrial gene (16S). Cmos and Rag2 sequences presented little to none genetic variability, while 16S allowed us to build a haplotype network. We identified nine haplotypes across mainland Ecuador, two of which are also present in Galapagos. Low genetic diversity between insular and continental populations suggests that the introduction of G.caudiscutatus on the Islands is relatively recent. Due to the widespread geographical distribution of mainland haplotypes, it was not possible to determine the source population of the introduction. This study represents the first exploration of the genetic diversity of Gonatodescaudiscutatus, utilising genetic tools to gain insights into its invasion history in the Galapagos.

Colonization routes uncovered in a widely introduced Mediterranean gecko, Tarentola mauritanica

In this study, we aimed to understand the contemporary and ancient colonization routes of the Moorish gecko, Tarentola mauritanica, using simple sequence repeats. By analyzing the genetic diversity of populations in different regions, we found that Morocco is the genetic diversity hotspot for the species, followed by the Iberian Peninsula. However, historical gene flow estimates identified the Iberian Peninsula, not Morocco, as the primary contributor of colonizing individuals, along with continental Italy to a lesser extent. Currently, mainland Italy is the main source of introduced individuals, likely due to the plant nursery trade. The study suggests that human-facilitated introductions from various geographical origins, with numerous regions colonized through continental Italy during two distinct periods, are responsible for the recurrent entry of individuals belonging to the European lineage of T. mauritanica into the Mediterranean and Macaronesia. These findings can inform better monitoring surveys and conservation programs by identifying putative current colonization routes of alien species.

A New Invasion of the Common Slider on a Mediterranean Island (Lesvos, Greece): A Potential Threat to Native Terrapin Populations?

Island wetlands are considered crucial to biodiversity due to their unique ecological, biogeographical, and socioeconomic dynamics. However, these habitat types are particularly vulnerable to invasion; invasive species can cause severe ecological, evolutionary, and epidemiological impacts on native species. One of the most important invasive species, the common slider Trachemys scripta, an opportunistic inhabitant of freshwater habitats, has been released in multiple localities across Greece in recent years, and has expanded its range through random and unintentional releases in the Aegean islands. Since its first documented record on the island of Crete in 1998, the species has been observed on six more islands. Here, we report, for the first time, two subspecies of the common slider (T. scripta scripta and T. scripta elegans) on the wetlands of the island of Lesvos. We discuss the potential threats to native terrapins and we examine whether the introduction of this invasive species has affected native terrapins by monitoring their populations for 12 consecutive years (2010–2022). We found the common slider in 3 out of 110 wetlands surveyed. At one site, we document the presence of invasive terrapins belonging to two different subspecies. In all surveyed wetlands, we found stable populations of the two native freshwater terrapins, Mauremys rivulata and Emys orbicularis, with the first species found in much larger populations than the second. Despite these reassuring findings, the presence of this introduced species on the island of Lesvos raises serious concerns regarding its negative effects on the local terrapin populations. We propose that systematic and thorough monitoring of insular wetlands, as in the case of Lesvos, should be adopted on other islands as well, with priority on those where the common slider has been recorded.

Status of the largest extant population of the critically endangered Aeolian lizard Podarcis raffonei (Capo Grosso, Vulcano island)

The Aeolian wall lizard Podarcis raffonei is an island endemic that survives only on three tiny islets, and on the Capo Grosso peninsula of the Vulcano island, thus is among the European vertebrates with the smallest range and one of the most threatened by extinction. This species is declining due to competition and hybridization with the non-native lizard Podarcis siculus, but a regular monitoring program is lacking. Here we assessed the size and status of the Capo Grosso population of P. raffonei on Vulcano. In September 2015 we captured 30 individuals showing the typical brown phenotype of P. raffonei, while one single male showed a green phenotype, apparently intermediate between P. raffonei and the non-native Podarcis siculus. In May 2017, only 47% of 131 individuals showed the typical brown phenotype (P. raffonei-like) and 53% showed the green phenotype (P. siculus-like). Based on N-mixture models and removal sampling the estimated size of the Capo Grosso population was of 800–1300 individuals in 2017, being similar to 2015; available data suggest that the total range of the species could be as small as 2 ha. The frequency of individuals with the typical P. raffonei phenotype dramatically dropped between two samplings with a parallel increase of individuals displaying the green phenotype. Observation on outdoor captive-bred individuals demonstrates plasticity for colouration in P. raffonei individuals from Capo Grosso, with several individuals showing the typical brown pattern in September 2017 and a green pattern in March 2021. Non-exclusive hypotheses, including hybridization with P. siculus and plasticity in colour pattern of P. raffonei, are discussed to explain the phenotypic shifts of the P. raffonei population of Capo Grosso. While genomic evidence is required to reach conclusions and investigate eventual hybridization, it is urgent to undertake a programme for the monitoring and management of this lizard.

Trophic niche changes associated with the eradication of invasive mammals in an insular lizard: an assessment using isotopes

Invasive species are a major threat to island biodiversity, and their eradications have substantially contributed to the conservation of island endemics. However, the consequences of eradications on the trophic ecology of native taxa are largely unexplored. Here, we used the eradication of invasive black rats Rattus rattus and European rabbits Oryctolagus cuniculus from the Berlenga Island, in the western coast of Portugal, as a whole-ecosystem experiment to investigate the effects of the eradication of invasive mammals on the trophic niche and body dimensions of the island-restricted Berlenga wall lizard Podarcis carbonelli berlengensis over a 2-year period. Our results suggest an expansion of the isotopic niche and an intensification of the sexual dimorphism of the lizard following mammal eradication. Additionally, we found considerable variability in isotopic niche across the island and detected evidence of sex-specific and season-modulated nutritional requirements of this threatened reptile. Our findings support that the eradication of 2 of the planet’s most problematic invasive vertebrates led to changes in the lizard trophic niche and sexual dimorphism in just 2 years. This suggests that the ecological pressures—for example, prey availability and habitat structure—to which lizards are exposed have substantially changed post-eradication. Our study emphasizes the scientific value of island eradications as experiments to address a wide range of ecological questions and adds to the increasing body of evidence supporting substantial conservation gains associated with these restoration interventions.

Fossil-calibrated time tree of Podarcis wall lizards provides limited support for biogeographic calibration models

Podarcis wall lizards are endemic to the Mediterranean Basin where they represent the predominant reptile group. Despite being extensively used as model organisms in evolutionary and ecological studies their phylogeny and historical biogeography are still incompletely resolved. Moreover, molecular clock calibrations used in wall lizard phylogeography are based on the assumption of vicariant speciation triggered by the abrupt Mediterranean Sea level rise at the end of the Messinian salinity crisis (MSC). However, the validity of this biogeographic calibration remains untested. In this study we inferred a robust time tree based on multilocus data and fossil calibrations using both gene concatenation and species-tree approaches and including models with gene-flow. We found five deeply divergent, geographically coherent, and well-supported clades comprising species from i) Iberian Peninsula and North Africa; ii) Western Mediterranean islands, iii) Sicilian and Maltese islands; and iv-v) Balkan region and Aegean islands. The mitochondrial tree shows some inconsistencies with the species tree that warrant future investigation. Diversification of main clades is estimated in a short time frame during the Middle Miocene and might have been associated with a period of global climate cooling with the establishment of a marked climatic zonation in Europe. Cladogenetic events within the main clades are scattered throughout the time tree, from the Late Miocene to the Early Pleistocene, suggesting that speciation events in wall lizards reflect a complex interplay between regional topography, climate and geological history rather than a shared major climatic or paleogeographic event. Our absolute time estimates, as well as a relative dating approach, demonstrate that the assumption of a causal link between sea-level rise at the end of the MSC and the diversification of many island endemics is not justified. This study reinforces the notion that multiple dispersal and vicariant events, at different time frames, are required to explain current allopatric distributions and to account for the historical assembly of Mediterranean biota, and cautions against the use of biogeographic calibrations based on the assumption of vicariance.

An odyssey out of Africa: an integrative review of past and present invasions by the Mediterranean tree frog (Hyla meridionalis)

An illustration of the human footprint on biodiversity are the faunal movements that have accompanied commercial and cultural exchanges between civilizations throughout history. In this article, we provide an integrative review of biogeographical and archaeological knowledge to understand these processes for the Mediterranean tree frog (Hyla meridionalis), an African species that has reached several regions of south-western Europe and associated islands. By re-analysing molecular (multilocus mitochondrial and genome-wide markers) and bioclimatic (ecological niche modelling) data, we give a comprehensive picture of the genetic diversity, structure and environmental suitability of H. meridionalis across its natural and exotic ranges, which in turn offer specific clues to the putative routes of colonization and associated events. Long-term monitoring efforts suggest northwards shifts of local range margins, potentially due to global warming, and we further demonstrate that this species is the most frequent amphibian to travel via the food supply chain in Western Europe. High dispersal ability, ecological tolerance and proximity to human settlements have made H. meridionalis a recurrent witness to the complexity and diversity of the civilizations that ruled the Western Mediterranean.

The possible origin of the common wall lizard, Podarcis muralis (Laurenti, 1768) in Ukraine

The phylogenetic relationships and possible origin of a putative non-native population of Podarcis muralis in Ukraine were assessed based on sequences of the mitochondrial gene cytochrome b. Phylogenetic analysis showed that the Ukrainian lizards belong to two distinct mitochondrial lineages (haplogroups), both occurring within the Central Balkan clade, which includes most of central and south-eastern European populations. From overall three detected Ukrainian haplotypes, one haplotype share same genetic signal with the hyplotype from the locality Bjala (Bulgaria), the other two are unique for Ukrainian population. Two of haplotypes correspond with haplogroup covering large geographic region of Bulgaria, Serbia, and Romania. These results reinforce previous findings that the species has the ability to establish new populations out of its native range. While most introductions to Germany and Britain have been deliberate, it appears likely that human transport of goods via the Danube river of goods is responsible for the range expansion into Ukraine.